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<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>InAppWebViewOnJsBeforeUnloadTest</title>
    </head>
    <body>
        <h1>InAppWebViewOnJsBeforeUnloadTest</h1>
        <script>
            window.addEventListener('beforeunload', function (e) {
              e.preventDefault();
              e.returnValue = '';
            });
            setTimeout(function() {
                window.location.href = 'https://flutter.dev';
            }, 500);
        </script>
    </body>
</html>